1. Field of the Invention
This invention relates to computer graphics systems and more specifically to area of interest display systems as for use in training simulators.
2. Discussion of the Prior Art
Area of interest (AOI) display systems are well known in the prior art as disclosed, for example, in U.S. Pat. No. 4,348,186, Harvey et al. and also in U.S. Pat. No. 4,634,384, Neves et al. Essentially, the systems combine and blend a high resolution, small field of view image (inset) with a wide field, low resolution image (background). For example, a trainee, seated in a flight simulator sees a wide field of view display to simulate the view of an actual flight pattern. Consequently, a trainee can experience specific flight routes or patterns with considerable realism while seated in a training simulator.
It has been recognized in the past that as a result of limitations in human visual perception a considerable portion of a wide field of vision display may be of relatively poor quality and still attain substantial realism. The key is to inset a high resolution image in the low resolution background image at the viewer's area of interest. As recognized in the past, such AOI systems take advantage of the fact that the high resolution viewing area of the eye (fovea) is relatively small. Specifically, as the fovea of a normal eye subtends an angle only of about two degrees, the high resolution inset image can be relatively small in relation to the low resolution background or panoramic image.
A previously recognized problem in producing area of interest displays has been avoiding visible effects at the border between the two images. Considerable effort has been expended attempting to avoid incongruities at the transition from the high resolution image to the low resolution image that are disturbing to the viewer. For example, the problem was recognized and considered in U.S. Pat. No. 4,634,384, "Head and/or Eye Tracked Optically Blended Display System", Neves et al.
Although various solutions have been proposed to accomplish a visually acceptable transition between the images in an AOI display, a need exists for an economical and effective process and apparatus to accomplish that end. In that regard, it is desirable to avoid the need for high precision optical alignment, exotic filtering or video systems requiring extensive hardware or critical operating requirements. In a related context, it is noteworthy that techniques involve substantial problems in attaining optical masks using proper sizing and proper optical density falloff. In that regard, alignment problems can be reduced by using a mirror image-combining structure. However, another problem is introduced because no technique is known to grade the reflectance of the mirror edge so that it gives equal optical control in both transmission for the background and reflectance for the inset. Such control is required for smooth blending at the boundary. Thus, the continuing nee, d exists for an improved system to solve the problem.